An electric vehicle or a plug-in hybrid vehicle includes: an inverter device to drive a motor with a high-voltage storage battery for power drive; and a low-voltage storage battery to operate auxiliary machines such as a light and a radio of the vehicle. This kind of vehicle is mounted with a DC-DC converter device that performs power conversion from the high-voltage storage battery to the low-voltage storage battery or power conversion from the low-voltage storage battery to the high-voltage storage battery.
The DC-DC converter device includes a high-voltage side switching circuit to convert high-voltage DC voltage to AC voltage, a transformer to convert high AC voltage to low AC voltage, and a low-voltage side rectifier circuit to convert low-voltage AC voltage to DC voltage. In such a DC-DC converter device that converts the voltage by switching a semiconductor device, switching noise generated by switching is needed to be suppressed and a noise filter is needed to be mounted on an output unit.
The DC-DC converter is downsized year after year, and downsizing of the noise filter to be mounted is also demanded. As an example of such downsizing, there is a known structure disclosed in PTL 1, for example. The invention disclosed in PTL 1 provides an LC filter device that can have multistage connection by forming a structure in which a coil portion can be integrated.